Understanding HRV
The field guide.
Short, accurate, opinionated answers to the questions people actually ask about heart rate variability.
The pillars
What is HRV, really?
The beat-to-beat variation in your heartbeat, explained without the wearable-marketing fluff.
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What counts as a 'good' HRV?
Why benchmarks are useless without context, and the only comparison that actually matters.
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How to actually improve your HRV
The five interventions with the strongest evidence — ranked by how much they move the needle.
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HRV by age
Approximate norms, why they're misleading, and how to compare yourself to yourself.
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What moves HRV
How alcohol affects HRV
The cleanest dose-response curve in the data. One drink, two drinks, the whole arc.
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How sleep determines HRV
The single largest input to overnight HRV. Stages, debt, timing, and where breathing fits.
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How stress shows up in HRV
Acute vs chronic stress produce different HRV signatures. Confusing them leads to wrong interventions.
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HRV and training
Readiness, recovery, overreaching. What HRV-guided training actually does — and doesn't.
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Low HRV: causes ranked
The common reasons HRV drops, ordered by how quickly each one tends to resolve.
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RMSSD vs SDNN
Why your Apple Watch HRV doesn't match your Oura HRV. The two metrics, plainly.
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The vagus nerve and HRV
The autonomic plumbing behind everything on this site. Plus honest framing on polyvagal theory.
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How to monitor HRV
Two different questions — state-now vs trend — and which device answers each. Hardware spectrum, practical setup, when to stop monitoring daily.
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Find your resonance frequency
Six breaths per minute is a population average, not your number. The clinical assessment protocol, an equipment-free approximation, and a wrist-based version.
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The BOLT score
A breath-hold measured to the first urge, not the limit. The one progress metric that needs no wearable — plus an honest read on its evidence.
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